Method for stabilising soils, more specifically soils excavated from trenches using a calcium-magnesium composition

Abstract

The invention relates to a method for stabilising soils, the method comprising the steps of excavating the material and gathering the latter, supplying a calcium-magnesium compound, mixing the calcium-magnesium compound with the excavated material to form a treated material, backfilling, compacting and forming a soil having an immediate bearing index of 5% or higher, the invention being characterised in that the supply step is a step of supplying a calcium-magnesium compound and an organic additive, the method comprising a step of hardening the treated material to form the stabilised soil having a compressive strength Rc of 2 MPa or less after 28 days.

Description

[0001] x yPROCESS FOR STABILIZING SOILS, MORE PARTICULARLY SOILS EXCAVATED FROM TRENCHES USING A CALC-MAGNESIAN COMPOSITION

[0002] This iinnvveennttiioonn ssee relates to a soil improvement process commonly called soil stabilization, more particularly of soils excavated from trenches, as well as to a calco-magnesium composition usable in this application.

[0003] More specifically, the method of stabilizing soils, more particularly soils excavated from trenches, comprises: a) Excavation of material to form one or more trenches and collection of the excavated material which has a predetermined water content, b) Supply of calco-magnesium compound to the excavated material, c) Mixing of the calco-magnesium compound with the excavated material to form a treated material having a water content lower than that of the excavated material, d) Backfilling with the treated material of the trench(es) after laying the element(s) to be buried, e) Compacting of the treated material placed during backfilling, f) Formation of a soil having an immediate bearing index greater than or equal to 5%.

[0004] Soil treatment with a calcium-magnesium compound is a technique widely used in civil engineering that allows unsuitable soils (usually fine clayey-sandy or silty-clayey soils) to be reused in construction, particularly in embankments. The calcium-magnesium compound thus dries the soil and improves its compaction, which makes it possible to achieve the desired bearing capacity.

[0005] Soil treatment with a calcium-magnesium compound such as lime has short, medium and long-term effects. In the short term, soil improvement results in a drying effect, a flocculation effect of clay particles, improved compaction behavior and an increase in bearing capacity, while in the medium and long term, a stabilized soil shows a significant increase in the strength of the soil-forming material, due to the pozzolanic reaction between the clay minerals, especially the silico-aluminous elements, and the added lime.

[0006] Soil treatment technology is used to facilitate the direct reuse of excavated soils, particularly clay-silt and wet plastics, to avoid dumping and storing them in landfills, while dry sand or soil would be brought to the site for backfilling. The technology enables a circular economy in the earthmoving sector.

[0007] For applications requiring possible re-excavation of the treated soil after months or years, the disadvantage of current technology is the excessive increase in the strength of the soil-forming material, which makes excavation impossible manually or with light equipment.

[0008] In trench construction, the excavated soils are generally damp or even saturated with water. These soils are then treated with lime to dry, flocculate, and allow direct reuse in backfilling the trenches. When using freshly excavated soils, high doses of lime are used to accentuate the drying of the soils, allowing direct reuse of the treated soils, but these high doses of lime required for drying subsequently lead to hardening between the lime and the clay minerals, resulting in a material that is too rigid. The lime-treated soil then develops characteristics that are fundamentally different from the surrounding and original soil. The consequences are problems during possible re-excavation, the risk of cracking of pipes, and the rupture of material interfaces.

[0009] US 5716448 describes a process in which excavated soil is transformed into liquid backfill material or mortar by adding a hydraulic solidifying agent (cement or hydraulic lime) and a fluidizing agent (water) with additives. As additives, this document describes the addition of sugars and a cement dispersing agent.

[0010] Hydraulic binders known to those skilled in the art harden by themselves in the presence of water. The calcium silicates in the hydraulic binder react with water to form hydrated calcium silicate (CSH) phases.

[0011] According to this document, the resulting mortar must retain an appropriate degree of fluidity for a substantial time to facilitate placement (up to 90 min) as well as excellent minimum final strength (measured after 7 and 28 days), and exhibit little or no cracking upon drying.

[0012] A detailed analysis of this document reveals that when cement is used as a hydraulic binder, in the presence of 1.5% by weight of starch syrup, the compressive strength measured at 7 and 28 days respectively is 3.04 MPa and 8.43 MPa. Similar results are obtained with glucose. Although lime is indicated as a hydraulic material, there is no example in this document illustrating lime as a hydraulic binder. Document JPS59-84972 describes the use of a soil stabilizing composition which makes it possible to delay solidification and hardening initially, at the time of placement, but to quickly achieve the desired minimum compressive strength in a later phase.

[0013] The soil stabilizing composition consists of 0.1 to 10 parts by weight of saccharides per 100 parts by weight of a cement / lime component which is a mixture of cement and lime in cement / lime weight proportions of 99:1 to 70:30.

[0014] The saccharide may be sucrose, glucose, fructose, galactose or maltose, black molasses, brown sugar or the like. An oxycarboxylic acid may be added and in this case the amount of saccharide and oxycarboxylic acid remains between 0.1 and 10 parts by weight of saccharides per 100 parts by weight of a cement-lime component. On the other hand, the saccharide content is between 5 and 60% by weight relative to the weight of lime.

[0015] According to this document, the lime content must be limited otherwise the compressive strength in the later phase (measured at 28 days) is insufficient.

[0016] As can be seen, the work undertaken according to these previous documents focuses on maintaining short-term workability by delaying setting and initial hardening to improve handling of the treated soil at the time of its placement, aiming to maintain a minimum subsequent hardening. They do not concern the control of hardening and compressive strength in the later phase for a longer duration.

[0017] The invention aims to overcome the disadvantages of the state of the art by providing a method for stabilizing soils, more particularly soils excavated from trenches, ensuring a short-term improvement in a few hours (reduction of the water content and flocculation leading to sufficient immediate bearing capacity), comparable to that obtained using standard quicklime (aerial type, as defined according to standard EN 459-1 paragraph 4.3.1), while controlling the reaction between the calco-magnesium compound (lime) and the clay minerals leading to a moderate development of the resistance of the material in the medium and long term.

[0018] The invention aims to control the hardening and compressive strength to a maximum value over time (> several months or years) and is therefore opposed to the prior arts cited above, which aim for a minimum value over time over a shorter period of time.

[0019] To solve this problem, there is provided according to the invention a method as indicated at the beginning characterized in that said feed of calco-magnesium compound is a feed of a calco-magnesium compound and an organic additive together in the form of a calco-magnesium composition or separately, in which the organic additive is chosen from saccharides and their derivatives, such as for example, monosaccharides, disaccharides, oligosaccharides and polysaccharides and their derivatives, more particularly galactose, mannose, xylose, glucose, fructose, saccharose, in particular sucrose, erythrose, threose, allose, trehalose, starch, modified or hydrolyzed starch, inverted sugar syrup, arabinose, ribose, maltose, lactose, cellulose, modified cellulose, maltotriose and raffinose, alcohol saccharides, such as sorbitol, glucitol, erythrol, lactitol, maltitol, or xylitol,carboxylic acids and their salts, more particularly uronic or aldonic acids, such as gluconic acid or sodium gluconate, inulin, or modified inulin, pectins, dextrins, and cyclodextrins and mixtures thereof, and in that the method further comprises hardening the treated and compacted material, after the step of compacting the treated material, to form a stabilized soil which has a compressive strength Rc less than or equal to 2 MPa, preferably less than 1.5 MPa, more preferably less than 0.7 MPa, and greater than or equal to 0.1 MPa, preferably greater than or equal to 0.2 MPa, after 28 days, advantageously at 40°C.,

[0020] As can be seen, the method according to the invention allows to control the hardening in a later phase by allowing the stabilized soil to have a compressive strength Rc not exceeding 2 MPa after 28 days at 40°C, whereas a standard lime treatment generates a compressive strength Rc of 3 MPa or more after 28 days at 40°C, and this, without compromising the immediate load-bearing capacity.

[0021] Thus, the method according to the invention makes it possible to treat excavated soils without having to use other soils as raw materials. Furthermore, when it is necessary to excavate the stabilized soil obtained by the method according to the invention again, this stabilized soil can easily be recovered, and possibly be treated again according to the method according to the invention, depending on the user's needs.

[0022] This compressive strength is measured by simulating the process in the laboratory at the Proctor optimum.

[0023] The Proctor optimum is determined by the normal Proctor test described in standard EN13286-2 (“Unbound and hydraulically bound mixtures - Part 2: Test methods for laboratory reference density and water content - Proctor compaction”). The Proctor optimum designates the water content for which compaction leads to a maximum dry density which therefore corresponds to a state of maximum compactness and a maximum resistance capacity to a defined energy. In the context of the present invention, compacted specimens in CBR molds, with dimensions of 152 mm (height) and 152 mm in diameter (according to standard NF P 94 093) were produced with a soil sample treated according to the invention, treated with lime or untreated.

[0024] The immediate bearing index (IPI) measures the punching resistance of the soil studied. It characterizes the soil's ability to allow, in particular, the movement of machinery on site. The immediate bearing index (IPI) expresses in % the ratio between the pressures producing at the same time a given sinkage in the soil tested and on the other hand in a standard material. By definition, this index corresponds to the greater of the two values ​​obtained by applying the following formulas according to standard EN 13286-47:

[0025] In addition, the cylindrical punch that applies the force should preferably have a diameter of (50 ± 0.5) mm (EN 13286-47).

[0026] The specimens are made in the CBR mold (California Bearing Ratio) by normal Proctor compaction test and are placed in the IPI press system with a sinking speed of 1.27 mm / min. Curves of pressure as a function of sinking are obtained. The curves are possibly correlated and the IPI is calculated by taking the maximum between the IPI25 and IPI50 values. The test is described in the standard EN 13286-47 ("Unbound and hydraulically bound mixtures - Part 47: Test method for the determination of California bearing ratio, immediate bearing index and linear swelling"). The simple compression test is carried out according to the standard NF EN 13286-41. It consists of subjecting a specimen to an axial force until rupture. The simple compressive strength Rc is defined as the stress measured at rupture. The apparatus used for this test is a press that meets the criteria of the standard EN 13286-41.

[0027] The specimens of natural soil or treated soil are placed between the two parallel plates of the press. The axis of the specimen is orthogonal to the plates. The application of the load is in accordance with the aforementioned standard EN 13286-41. The maximum force experienced by the specimen is recorded. The simple compressive strength is then calculated according to the following equation: where:

[0028] Rc (N / mm 2 or MPa): simple compressive strength,

[0029] F (N): maximum force on the specimen,

[0030] Ac (mm 2 ): cross-sectional area of ​​the specimen.

[0031] The simple compression test is carried out on at least two specimens. The simple compressive strength of a sample is the arithmetic mean of the values ​​obtained.

[0032] The 28-day compression test is carried out by keeping the specimens under well-defined temperature conditions, such as 20°C or 40°C. The temperature of 40°C will be preferred because the result obtained reflects the performance for a longer period of time, which makes it possible to simulate long-term curing (more than one year).

[0033] During the 28-day curing period, the specimens are stored hermetically in plastic film and a plastic bag to maintain the water content of the specimen constant. Storage at 40°C is carried out in a climatic chamber. The specimens are removed from the bag and plastic film just before the simple compression test.

[0034] Furthermore, according to the present invention, the soil treatment steps do not require special equipment or other practical modifications, the calco-magnesium compound as well as the organic additive are fed with a dosage in the same range as standard quicklime, which allows not to disrupt application practices on construction sites. However, the method according to the present invention allows easier re-excavation of the soil-forming materials, possibly manually or with light equipment, limiting the risks of damage to surrounding elements, such as pipes or cables in trench applications, including cracking of the pavement covering the newly filled trench.

[0035] In a particular embodiment of the present invention, the calco-magnesium compound of the calco-magnesium composition comprises quicklime or a quicklime compound having an available CaO content of at least 40% by weight, preferably at least 50% by weight, more particularly at least 65% by weight, preferably at least 70% by weight, more preferably still at least 75% by weight, advantageously at least 80% by weight, even more advantageously at least 90% by weight relative to the weight of the calco-magnesium compound.

[0036] The available CaO content is advantageously measured according to the EN 459-2 standard.

[0037] Preferably, different classes of quicklime are known to those skilled in the art, in particular classes CL 70, CL 80 and CL 90, as included in standard EN 459-2. These may respectively comprise an available CaO content greater than or equal to 55, greater than or equal to 65, greater than or equal to 80. These types of quicklime are also part of the present invention and may be combined with the embodiments described throughout this document.

[0038] According to a preferred embodiment, the calco-magnesium compound is quicklime, in particular aerial lime, having at least one of the following characteristics: a total CaO and MgO content greater than or equal to 70% by weight and an available CaO content greater than or equal to 55% by weight a total CaO and MgO content greater than or equal to 80% by weight and an available CaO content greater than or equal to 65% by weight a total CaO and MgO content greater than or equal to 90% by weight and an available CaO content greater than or equal to 80% by weight

[0039] Air lime is divided into two subfamilies, calcium lime (CL) and dolomitic lime (DL).

[0040] According to an advantageous embodiment, the calco-magnesium compound is quicklime, in particular aerial lime, having at least one of the following characteristics: a total CaO and MgO content of greater than or equal to 70% by weight, in particular greater than or equal to 80%, preferably greater than or equal to 88%, such as greater than or equal to 90%, very particularly greater than or equal to 95% by weight, and / or an available lime content of at least 50%, more particularly at least 55%, preferably at least 55%, more preferably still at least 70%, preferably greater than 85%, advantageously greater than 90%, more advantageously still greater than 93% by weight. According to a particularly advantageous embodiment, the calco-magnesium compound has a particle size of 99 less than 2 mm and a particle size of 50 greater than 3 μm, more particularly greater than 4 μm, and less than or equal to 90 μm.

[0041] In the context of the present invention, the calco-magnesium compound will preferably be quicklime, in particular aerial quicklime. Aerial lime is divided into two sub-families, calcium lime (CL) and dolomitic lime (DL). This embodiment makes it possible to further improve the results obtained. A combination between quicklime and the organic additive according to the invention will be advantageous in that it makes it possible to provide surprising results.

[0042] Quicklime is a solid mineral material, the chemical composition of which is mainly calcium oxide, CaO. Quicklime is commonly obtained by calcining limestone, which is mainly composed of CaCO3. Quicklime contains impurities, namely compounds such as magnesium oxide, MgO, silica, SiO2 or alumina, AI2O3, etc., in the amount of a few percent. It is understood that these impurities are expressed in the aforementioned forms but may actually appear in different phases. It also generally contains a few percent of residual CaCO3, called uncooked.

[0043] In addition, the skilled person is also familiar with dolomitic limes that may contain more than 5% MgO, in particular this value may be higher depending on the type of dolomitic lime. For example, a lime commonly called DL 85 may contain more than 30% by mass of MgO relative to the weight of the calco-magnesium compound, measured according to the EN 459-1 standard.

[0044] The expression "dry matter" preferably refers to fine clayey-sandy or silty-clayey soils. This material has a predetermined water content which depends on its nature, thus silt can contain between 15 and 25% by weight of water, or even more, sand can contain between 3 and 10% of water, or even more and clay can contain between 20 and 40% of water or even more, these contents being expressed as a function of the weight of the dry matter. It is obvious that any other type of soil can be used and is known to the person skilled in the art.

[0045] Advantageously, the soil targeted in the context of the present invention has an organic matter content of up to 6% by weight, as defined in Standard 16907-2: 2018 or NBN EN 16907-2: 2019. The present invention also preferably provides for the treatment of soil whose organic matter content is less than or equal to 2% by weight and / or also soils which are substantially free of organic matter, i.e. around 0.1% by weight, preferably 0% by weight. Thus, the organic matter content in the soil according to the invention can be between 0 and 6% by weight.

[0046] Thus, the addition of the calco-magnesium compound and the organic additive according to the invention to the excavated material makes it possible to reduce the water content of the treated material (read, dry out the treated material) which will thus have a lower quantity of water than the starting material.

[0047] The method according to the invention comprises a step of backfilling the trench(es) with the treated material after laying the element(s) to be buried. These elements to be buried can be any construction material that can be found underground, for example conduits (water, gas, etc.), pipes, technical ducts, fittings, sewer trenches.

[0048] Advantageously, it should be noted that the soil formed within the framework of the present invention has an immediate bearing index greater than or equal to 5%, preferably greater than or equal to 7%, more preferably greater than or equal to 10%.

[0049] It is also possible to achieve a lift index greater than or equal to 12% or greater than or equal to 15% or greater than or equal to 20% or greater than or equal to 25%, or greater than or equal to 30% for practical cases known to those skilled in the art. The immediate lift index may even exceed a value of 30%.

[0050] It should be noted that the above-mentioned lift index values ​​can be combined with each other.

[0051] Advantageously, in the method according to the present invention, said supply of calco-magnesium compound is carried out at a rate of 1 to 10% by weight, particularly 1 to 5% by weight, more particularly 1 to 3% by weight of the calco-magnesium compound relative to the weight of dry matter excavated.

[0052] In a particular embodiment of the method according to the invention, said additive is supplied at a rate of 2 to 10% by weight of organic additive, preferably 3 to 7% by weight of organic additive, more particularly 4 to 6% by weight or at a rate of an amount greater than 10% by weight and less than 20% by weight of organic additive, relative to the weight of calco-magnesium compound.

[0053] Particularly advantageously, according to the present invention, the organic additive is chosen from saccharides and their derivatives, such as, for example, monosaccharides, disaccharides, oligosaccharides and polysaccharides and their derivatives, more particularly galactose, mannose, xylose, glucose, fructose, saccharose, in particular sucrose, erythrose, threose, allose, trehalose, starch, modified or hydrolyzed starch, inverted sugar syrup, arabinose, ribose, maltose, lactose, cellulose, modified cellulose, maltotriose and raffinose, saccharide alcohols, such as sorbitol, glucitol, erythrol, lactitol, maltitol, or xylitol, carboxylic acids and their salts, more particularly uronic or aldonic acids, such as gluconic acid or sodium gluconate, inulin, or modified inulin, pectins, dextrins, and cyclodextrins and mixtures thereof.

[0054] According to a preferred embodiment of the present invention, the organic additive is chosen from saccharides and their derivatives, such as, for example, monosaccharides, disaccharides, oligosaccharides and polysaccharides and their derivatives, more particularly galactose, mannose, xylose, glucose, fructose, saccharose, in particular sucrose, erythrose, threose, allose, trehalose, starch, modified or hydrolyzed starch, inverted sugar syrup, arabinose, ribose, maltose, lactose, cellulose, modified cellulose, moltotriose and raffinose, saccharide alcohols, such as sorbitol, glucitol, erythrol, lactitol, maltitol, or xylitol, as well as mixtures thereof.

[0055] More particularly, according to the present invention, the calco-magnesium compound is quicklime, in particular air quicklime. Air lime is divided into two subfamilies, calcium lime (CL) and dolomitic lime (DL).

[0056] Preferably, air lime is defined more precisely in standard EN-459-1, relating to lime for construction.

[0057] According to this standard, the term lime means both calcium lime and dolomitic lime and includes calcium oxide and / or hydroxide, calcium-magnesium oxide and / or hydroxide produced by the thermal decomposition (calcination) of natural calcium carbonate (e.g. limestone, chalk, shells) or natural calcium-magnesium carbonate (e.g. dolomitic limestone, dolomite).

[0058] According to this standard, air lime is one of the above-mentioned limes, which combines and hardens with carbon dioxide present in the air. Air lime has no hydraulic properties. Air lime is divided into two subfamilies, calcium lime (CL) and dolomitic lime (DL).

[0059] In contrast, hydraulic lime is a building lime composed primarily of calcium hydroxide, calcium silicates, and calcium aluminates. It has the property of setting and hardening when mixed with or in contact with water and / or underwater. Reaction with atmospheric carbon dioxide is part of the hardening process. Hydraulic lime is divided into three subfamilies: natural hydraulic lime (NHL), formulated lime (FL), and hydraulic lime (HL).

[0060] Hydraulic lime is a binder made from lime and other materials such as cement, blast furnace slag, fly ash, and other suitable materials. It has the property of setting and hardening underwater. Atmospheric carbon dioxide contributes to the hardening process.

[0061] The air lime reacts, (1) with CO2 from the air to harden into CaCO3 or (2) by a pozzolanic reaction. The pozzolanic reaction occurs when the ash or clay of the pozzolanic material which contains silica and alumina are respectively activated or solubilized by the high pH generated by the lime in the soil and react with calcium to form hydrated calcium silicates. Other embodiments of the process according to the invention are indicated in the appended claims.

[0062] The present invention also relates to a powdery composition comprising a calco-magnesium compound and an organic additive, characterized in that said organic additive is present in the powdery composition in a quantity sufficient to form a stabilized soil, more particularly excavated soils, which has an immediate bearing index greater than 5% and a compressive strength Rc less than or equal to 2 MPa, after 28 days, preferably at 40°C.

[0063] Thus and preferably, the powdery composition which comprises a calco-magnesium compound and an organic additive can be mixed with a material, preferably an excavated material, such as soils, preferably moist soils, in particular silty or clayey or sandy-clayey soils.

[0064] In a particular embodiment, the composition has a t 60greater than 20 min, in particular greater than 30 min, in particular greater than 60 min, more particularly greater than 80 min, even more particularly greater than 100 min. Advantageously, the composition has a t 60 less than 150 min. All the above values ​​can be combined with each other.

[0065] Advantageously, the calco-magnesium compound is chosen from the group consisting of quicklime and a quicklime compound having an available CaO content of at least 40% by weight, preferably at least 50% by weight, more particularly at least 65% by weight, preferably at least 70% by weight, more preferably still at least 75% by weight, advantageously at least 80% by weight, even more advantageously at least 90% by weight, relative to the weight of the calco-magnesium compound.According to a preferred embodiment, the calco-magnesium compound is quicklime, in particular aerial lime, having at least one of the following characteristics: a total CaO and MgO content greater than or equal to 70% by weight and an available CaO content greater than or equal to 55% by weight a total CaO and MgO content greater than or equal to 80% by weight and an available CaO content greater than or equal to 65% by weight a total CaO and MgO content greater than or equal to 90% by weight and an available CaO content greater than or equal to 80% by weight.

[0066] According to an advantageous embodiment, the calco-magnesium compound is quicklime, in particular aerial lime, having at least one of the following characteristics: a total CaO and MgO content of greater than or equal to 70% by weight, in particular greater than or equal to 80%, preferably greater than or equal to 8%, such as greater than or equal to 90%, very particularly greater than or equal to 95% by weight, and / or an available lime content of at least 50%, more particularly at least 55%, preferably at least 55%, more preferably at least 70%, preferably greater than 85%, advantageously greater than 90%, more advantageously still greater than 93% by weight.

[0067] Air lime is divided into two subfamilies, calcium lime (CL) and dolomitic lime (DL).

[0068] According to a particularly advantageous embodiment, the calco-magnesium compound has a particle size of 99less than 2 mm and a particle size dso greater than 3 μm, more particularly greater than 4 μm, and less than or equal to 90 μm. Preferably, the organic additive is present in an amount of at least 2%, preferably at least 3%, more particularly at least 4% by weight, more particularly at most 10% by weight, preferably at most 7% by weight, more particularly at most 6% by weight or in an amount of between 10 and 20% by weight, relative to the weight of calco-magnesium compound.

[0069] The organic additive is chosen from saccharides and their derivatives, such as, for example, monosaccharides, disaccharides, oligosaccharides and polysaccharides and their derivatives, more particularly galactose, mannose, xylose, glucose, fructose, saccharose, in particular sucrose, erythrose, threose, allose, trehalose, starch, modified or hydrolyzed starch, inverted sugar syrup, arabinose, ribose, maltose, lactose, cellulose, modified cellulose, moltotriose and raffinose, saccharide alcohols, such as sorbitol, glucitol, erythrol, lactitol, maltitol, or xylitol, carboxylic acids and their salts, more particularly uronic or aldonic acids, such as gluconic acid or gluconate sodium, inulin, or modified inulin, pectins, dextrins, and cyclodextrins and mixtures thereof.

[0070] According to a preferred embodiment, the organic additive is advantageously chosen from saccharides and their derivatives, such as, for example, monosaccharides, disaccharides, oligosaccharides and polysaccharides and their derivatives, more particularly galactose, mannose, xylose, glucose, fructose, saccharose, in particular sucrose, erythrose, threose, allose, trehalose, starch, modified or hydrolyzed starch, inverted sugar syrup, arabinose, ribose, maltose, lactose, cellulose, modified cellulose, moltotriose and raffinose, saccharide alcohols, such as sorbitol, glucitol, erythrol, lactitol, maltitol, or xylitol, as well as mixtures thereof. More preferably still, the calco-magnesium compound is quicklime having at least one of the following characteristics: a total content of available CaO and MgO greater than 80% by weight and an available lime content of at least 70%.

[0071] According to a preferred embodiment, said calco-magnesium compound is quicklime, in particular aerial quicklime. Aerial lime is divided into two subfamilies, calcium lime (CL) and dolomitic lime (DL).

[0072] Other embodiments of the powdery composition according to the invention are indicated in the appended claims. It should be noted that all the characteristics which have been mentioned above for the process can also be combined with the preferred embodiments described for the composition according to the invention.

[0073] The present invention also relates to a product, possibly used in the field of construction, civil engineering, earthworks or in the stabilization of soils, in particular excavated soils. This product can be obtained by the process according to the invention, this product having a compressive strength Rc less than or equal to 2 MPa, after 28 days, preferably at 40°C.

[0074] As explained for the composition of the invention, all the characteristics which have been mentioned above for the process and / or the composition can also be combined with the preferred embodiments described for the product according to the invention.

[0075] Furthermore, the present document also targets a use of the powdery composition according to the invention for treating excavated material, preferably in the field of construction or civil engineering, in order to form a stabilized soil which has an immediate bearing index greater than 5% and a compressive strength Rc less than or equal to 2 MPa, after 28 days, preferably at 40°C.

[0076] As explained for the product of the invention, all the characteristics which have been mentioned above for the process and / or the composition and / or the product can also be combined with the preferred embodiments described for the use of the powdery composition according to the invention.

[0077] Other embodiments of the product and use according to the invention are indicated in the appended claims.

[0078] The notation dx represents a diameter, expressed in μm, measured by laser diffraction particle size analysis with methanol as the carrier solvent, with respect to which X% by volume of the measured particles or grains are smaller than or equal to this diameter. Before measurement, the sample is subjected in situ to ultrasound for 120 seconds to improve particle dispersion without risking particle breakage.

[0079] The reactivity of quicklime is generally characterized and measured by the procedure disclosed in the European standard EN459-2 (§ 6.6) and often quantified by the t 60 , time required to reach 60°C for a volume of water of 600 cm 3 initially at 20°C, from the addition of 150 g of quicklime.

[0080] Preferably, the calco-magnesium compound of the calco-magnesium composition is a quicklime, particularly an air quicklime. Air lime is divided into two subfamilies, calcium lime (CL) and dolomitic lime (DL).

[0081] Other characteristics, details and advantages of the invention will emerge from the description given below, without limitation and with reference to the drawings and examples. The invention relates to a method, a composition, a product and a use in the context of soil stabilization, preferably in the field of construction or civil engineering. The product is in particular composed of a mixture of quicklime (optionally partially combined with hydraulic binders) and an organic additive.The mixture is for example composed mainly (from 50 to more than 90%) of standard quicklime (possibly partially combined with calcium-based hydraulic binders) and from 2 to 10%, more particularly from 3 to 7%, more particularly from 4 to 6%, and even more particularly from 5% or in an amount of between 10 and 20% by weight of organic additive relative to the standard quicklime (possibly partially combined with calcium-based hydraulic binders).

[0082] The calco-magnesium composition according to the present invention is used for the treatment of soils, especially wet soils, especially silty or clayey or sandy-clayey soils, and it results in a reduction of the water content, flocculation of clay minerals and an immediate bearing capacity comparable to a standard treatment with quicklime. In the medium and long term, the composition according to the present invention controls the pozzolanic reaction ensuring a moderate increase in the strength of the material. This property facilitates possible excavation of the treated material after months or years manually or with light equipment, compressibility and similar behavior of the treated volume with the surrounding soils and limited strength development.

[0083] Control of the pozzolanic reaction is achieved by optimally adjusting the organic additive to (1) maintain the drying effect linked to the exothermic reaction of quicklime which hydrates to form calcium hydroxide,

[0084] (2) maintain the flocculation effect of calcium hydroxide on clay minerals,

[0085] (3) control the quantity of available (free) lime for

[0086] (a) increasing the pH for solubilization of silica and alumina from clay and silt contained in the treated soil, and

[0087] (b) carry out in a controlled manner the pozzolanic reaction leading to the development of resistance and modulus of elasticity E.

[0088] The manufacturing process of the calco-magnesium composition is preferably carried out by an industrial mixture of calco-magnesium compound, in particular quicklime with the organic additive in the lime plant, either in a mixing plant or subsequent mixing activity. Similarly, a two-component feed on a construction site with combined dosing of the calco-magnesium compound and the organic additive can be carried out.

[0089] In the examples referenced below, the following standards were used: the Immediate Lift index measured according to the standard

[0090] EN 13286-47 and / or NF P 94-078 and the compressive strength Rc can be measured according to standard EN 13286-41 and / or NF P94-077.

[0091] Examples.- 1

[0092] Comparative example - 1

[0093] A loamy soil (VBS = 2.59 g / 100g) is treated with 2% (relative to the dry mass of the soil) of standard quicklime - CL 90, available CaO = 91.2% and t 60 =5.2 min. The immediate bearing index (IPI) at a compaction water content corresponding to the Proctor optimum (wOPN = 16%) is equal to 33%.

[0094] The compressive strength Pc measured after curing (storage in a hermetically sealed environment) for 28 days at 40°C is equal to 3.88 MPa (wOPN=1 6%, dry density = 98.5% OPN).

[0095] Example according to the invention.- 1

[0096] The same soil is treated with 2% (relative to the dry mass of the soil) of the mixture according to the invention. The mixture is formed of a 95% calcium-magnesium compound (100% standard quicklime) and 5% sucrose. The immediate bearing index (IPI) at a Proctor optimum compaction water content (wOPN = 16%) is equal to 32%.

[0097] The compressive strength (Pc) measured after curing (storage in a hermetically sealed environment) for 28 days at 40°C is equal to 1 MPa (wOPN=1 6%, dry density=95% OPN). The 40°C test is generally recognized to simulate the long-term curing potential (several years).

[0098] As can be seen, the immediate load-bearing index of comparative example 1 is similar to that indicated in example 1 according to the invention. However, with regard to the compressive strength Pc after 28 days at 40°C, example 1 according to the invention indicates a Pc value of less than 2 MPa, which is particularly advantageous.

[0099] Examples.- 2

[0100] Comparative example - 2

[0101] The same soil from Example 1 is treated with 2% (relative to the dry mass of the soil) of the same quicklime from Example 1. The immediate bearing index (IPI), at a compaction water content of 20%, is equal to 24%.

[0102] The compressive strength measured after curing (storage in a hermetically sealed environment) for 28 days at 40°C is equal to 3.07 MPa (w=20%, dry density = 98.5% OPN).

[0103] Example according to the invention.- 2

[0104] The same soil is treated with 2% (relative to the dry mass of the soil) of the mixture according to the invention. The mixture is formed of a calcium-magnesium compound (100% standard quicklime) at 95% and 5% sucrose.

[0105] The immediate bearing index (IPI), at a compaction water content of 20%, is equal to 18%.

[0106] The compressive strength (Rc) measured after curing (storage in a hermetically sealed environment) for 28 days at 40°C is equal to 1 MPa (w=20%, dry density=95% OPN). Testing at 40°C is generally recognized to simulate long-term curing potential (several years).

[0107] As can be seen, the immediate load-bearing index of comparative example 2 is similar to that indicated in example 2 according to the invention. However, with regard to the compressive strength Rc after 28 days at 40°C, example 2 according to the invention indicates an Rc value of less than 2 MPa, which is particularly advantageous.

[0108] Examples.- 3

[0109] Comparative example - 3

[0110] A loamy soil (VBS = 2.5 g / 100 g, passing at 80 μm = 97 %) is treated with 2 % (relative to the dry mass of the soil) of quicklime 0 / 90 μm (available CaO = 94.5 %, t60 = 2.4 min). The immediate bearing index (IPI), at a water content before treatment of 20 %, is 9 %.

[0111] Under the same water content conditions, the compressive strength measured after curing (storage in a hermetically sealed environment) for 28 days at 40°C is equal to 2.92 MPa (dry density = 95% OPN).

[0112] Example according to the invention.- 3

[0113] The same soil is treated with 2.1% (based on the dry mass of the soil) of the mixture. The mixture consists of a 95% calcium-magnesium compound (100% standard quicklime) and 5% sucrose.

[0114] The immediate bearing index (IPI) at a pre-treatment water content of 20% is equal to 9%.

[0115] The compressive strength (Rc) measured after curing (storage in a hermetically sealed environment) for 28 days at 40°C is equal to 1.69 MPa (dry density=95% OPN).

[0116] As can be seen, the immediate load-bearing index of comparative example 3 is similar to that indicated in example 3 according to the invention. However, with regard to the compressive strength Rc after 28 days at 40°C, example 3 according to the invention indicates an Rc value of less than 2 MPa, which is particularly advantageous.

[0117] It is understood that the present invention is in no way limited to the embodiments described above and that many modifications may be made thereto without departing from the scope of the appended claims.

Claims

AMENDED CLAIMS received by the International Bureau on September 7, 2023 (07.09.223) 1. A method for stabilizing soils, more particularly soils excavated from trenches, comprising: a) Excavating material to form one or more trenches and collecting the excavated material, which has a predetermined water content; b) Adding a calcium-magnesium compound to the excavated material; c) Mixing the calcium-magnesium compound with the excavated material to form a treated material having a water content lower than that of the excavated material; d) Backfilling the trench(s) with the treated material after placing the element(s) to be buried; e) Compacting the treated material placed during backfilling; f) Forming a soil with an immediate bearing capacity index greater than or equal to 5%, characterized in that said addition of calcium-magnesium compound is an addition of a calcium-magnesium compound and an organic additive together in the form of a calcium-magnesium composition or separately.in which the organic additive is selected from saccharides and their derivatives, such as monosaccharides, disaccharides, oligosaccharides and polysaccharides and their derivatives, more particularly galactose, mannose, xylose, glucose, fructose, sucrose, in particular sucrose, erythrose, threose, allose, trehalose, starch, modified or hydrolyzed starch, invert sugar syrup, arabinose, ribose, maltose, lactose, the, cellulose, modified cellulose, maltotriose and raffinose, saccharide alcohols, such as sorbitol, glucitol, erythrol, lactitol, maltitol, or xylitol, carboxylic acids and their salts, more particularly uronic or aldonic acids, such as gluconic acid or sodium gluconate, inulin, or modified inulin, pectins, dextrins, and cyclodextrins and mixtures thereof, and in that the process further comprises a hardening of the treated and compacted material, after the compaction step of the treated material to form a stabilized soil which has a compressive strength Rc less than or equal to 2 MPa, after 28 days.

2. A method for stabilizing soils, more particularly soils excavated from trenches according to claim 1, wherein the calcium-magnesium compound of the calcium-magnesium composition is quicklime or a quick compound having an available CaO content of at least 40% by weight, preferably at least 50% by weight, more particularly at least 65% by weight, preferably at least 70% by weight, more preferably still at least 75% by weight, advantageously at least 80% by weight, more advantageously still at least 90% by weight relative to the weight of the calcium-magnesium compound.

3. Method for stabilizing soils, more particularly soils excavated from trenches according to claim 1 or claim 2, wherein said feeding of calcium-magnesium compound is carried out at a rate of 1 to 10% by weight, more particularly of 1.5 to 5% by weight of the calcium-magnesium compound relative to the weight of dry matter excavated.

4. A method for stabilizing soils, more particularly soils excavated from trenches, according to any one of claims 1 to 3, wherein said additive is fed with 2 to 10% by weight of organic additive, preferably 3 to 7% by weight of additive organic, more particularly 4 to 6% by weight or at a rate of more than 10% by weight and less than 20% by weight of organic additive, relative to the weight of calcium-magnesium compound.

5. A method for stabilizing soils, more particularly soils excavated from trenches according to any one of claims 1 to 4, wherein the calcium-magnesium compound is quicklime, in particular aerial quicklime.

6. A powdered composition comprising a calcium-magnesium compound and an organic additive, characterized in that said calcium-magnesium compound is quicklime and said organic additive is present in the powdered composition in sufficient quantity to form a stabilized soil, more particularly excavated soils, which has an immediate bearing capacity index greater than 5% and a compressive strength Rc less than or equal to 2 MPa, after 28 days, preferably at 40°C, and in which the organic additive is selected from monosaccharides, disaccharides, oligosaccharides and polysaccharides and their derivatives, more particularly galactose, mannose, xylose, glucose, fructose, sucrose, in particular sucrose, erythrose, threose, allose, trehalose, starch, modified or hydrolyzed starch, inverted sugar syrup, Arabinose, ribose, maltose, lactose, cellulose, modified cellulose,maltotriose and raffinose, saccharide alcohols such as sorbitol, glucitol, erythrol, lactitol, maltitol, or xylitol, carboxylic acids and their salts, particularly uronic or aldonic acids such as gluconic acid or sodium gluconate, inulin or modified inulin, pectins, dextrins, and cyclodextrins and mixtures thereof.

7. Powdered composition according to claim 6 characterized in that the composition has a t 60 more than 20 minutes, especially more than 30 minutes, especially more than 60 minutes, plus particularly greater than 80 min, even more particularly greater than 100 min.

8. Powdered composition according to claim 6 or 7, wherein the calcium-magnesium compound is selected from the group consisting of quicklime and a quick compound having an available CaO content of at least 40% by weight, preferably at least 50% by weight, more particularly at least 65% by weight, preferably at least 70% by weight, more preferably still at least 75% by weight, advantageously at least 80% by weight, more advantageously still at least 90% by weight, relative to the weight of the calcium-magnesium compound.

9. A powdered composition according to any one of claims 6 to 8, wherein the calcium-magnesium compound has a particle size of 99 less than 2 mm and a particle size of 50 greater than 3 μm, more particularly greater than 4 μm, and less than or equal to 90 μm.

10. Composition according to any one of claims 6 to 9, wherein the organic additive is present at a rate of at least 2%, preferably at least 3%, more particularly at least 4% by weight, more particularly at most 10% by weight, preferably at most 7% by weight, more particularly at most 6% by weight or at a rate of between 10 and 20% by weight, relative to the weight of the calcium-magnesium compound.

1. Powdered composition according to any one of claims 6 to 10, wherein the calcium-magnesium compound is quicklime having at least one of the following characteristics: a total available CaO and MgO content greater than 80% by weight and an available lime content of at least 70%.

12. Powdered composition according to any one of claims 6 to 11, wherein said calc-magnesium compound is aerial quicklime.

13. Product obtainable by the process according to any one of claims 1 to 5, having a compressive strength Rc less than or equal to 2 MPa, after 28 days, preferably at 40°C.

14. Use of the powder composition according to any one of claims 6 to 13 for treating excavated material to form a stabilized soil which has an immediate bearing capacity index greater than 5% and a compressive strength Rc less than or equal to 2 MPa, after 28 days, preferably at 40°C.

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